1. Field of Invention
This invention relates to a device giving a reading in increments of time for a given use of the remaining useful life of a storage battery used as a prime power source.
2. Description of the Prior Art
To determine the amount of the remaining charge for use in a storage battery such as a lead acid storage battery, requires a complex procedure.
One method is to use a hydrometer which draws electrolyte from each of the cells of the battery and makes a comparison with a specific gravity reading to determine the percentage of charge in the battery.
Another method in use is a highly accurate laboratory volt meter to measure open circuit voltage of each cell and compare the readings to a calibration chart.
Extreme skill is required in using a meter. For example, in a typical 12 volt battery, the full charge is approximately 12.7 volts and the completely discharged battery has a voltage of approximately 11.7 volts. The entire use range of the battery's voltage excursion is only one volt in 12.7 or on the order of only 8%. A standard metering instrument would be unable to measure such a narrow voltage excursion and provide meaningful results. The results would have to be matched against a calibration curve for the particular type of battery being used before the result could be meaningful to an unskilled operator.
It is desirable to have a device to give an accurate output reading stating the remaining useful life of a battery in increments of time for any given use to which the battery is put as a prime power source, or that is to say, as a sole power source.
In making reference to prior art devices, Wallace in U.S. Pat. No. 3,383,580, discloses a device for use only with a dry cell battery to indicate a remaining time period of use. However, the device is required to be used with a series voltage regulator and with a controlled output and must be tested in a closed circuit, that is while the battery is in use, and requires that both the load and the ambient temperature be known and constant. Such a device does not permit use with anything directly powered by the battery without the inclusion of a series voltage regulator. In connection with this, the voltage regulator for its own operation may drain off as much as 25% to 40% of the battery energy. Thus device is not applicable to wet cell or rechargeable batteries. There are severe limitations to the use of the Wallace device.
Juhasz in U.S. Pat. No. 4,104,580 discloses a battery testing apparatus to provide a reading of output voltage on a scale having a plurality of subdivisions for variations in temperature. Ambient temperature significantly affects a reading. Juhasz does not have a single specific reading irrespective of ambient temperature. Juhasz talks about measuring battery voltage such as when a starter is operated. The reading given relates only to the then existing voltage. Thus gives no knowledge as to the remaining charge in the battery. Further Juhasz refers to the remaining storage capacity of this battery or its ability to store a charge as being measured. This relates merely to the size of the container and not as to what is in it. Juhasz does not read clear conclusions. He appears to refer mainly to measurement of voltage and capacity and does not provide an understanding of the extent of the useful life remaining in a storage battery at any given time for a given use. Juhasz would appear to provide a voltage reading as an indication of the remaining charge in a battery. Such a reading does not indicate the charge remaining in a battery. It would appear that the best that Juhasz tells you is whether the battery is operational or should be replaced. The whole thrust of the invention herein is to indicate how much useful charge is in the battery. It is noted here that a battery as a power source to start up a gasoline engine, for example, merely has a starting application and a full charge is subsequently restored as with an alternator. Such a battery has a different design or construction than a storage battery used or a prime power source and such batteries have different operational requirements. Such batteries are excluded from consideration herein.